Flat cap

In electrical and electronic circuits, this refers to a phenomenon in which unintended oscillation occurs at a specific frequency due to design or wiring defects, affecting the functionality. It is synonymous with abnormal oscillation.

In an on-off feedback control circuit, when the controlled variable exceeds the target value and the manipulated variable changes from on to off, the controlled variable may then fall below the target value. When the manipulated variable is switched back from off to on, the controlled variable may again exceed the target value. This repeated behavior causes the controlled variable to fluctuate up and down around the target value.